Impact tool

ABSTRACT

Disclosed is a free-piston type, pneumatically operated impact tool comprising a tool cylinder and a pump cylinder both pneumatically and integrally connected. The reciprocation of the pump piston in the pump cylinder will cause the massive freepiston to rise and descend in the tool cylinder, and the freepiston will hammer the shank of the chisel at the end of the down stroke. The unique design of the pneumatic connection between the top spaces of the tool and pump pistons permits the use of a heavier free-piston, and hence the impact power will be accordingly increased.

O United States Patent 1191 1111 3,878,902

Matsuo Apr. 22, 1975 1 IMPACT TOOL 1.319.975 10/1919 Smith 173/1161.829.609 10/1931 Robinson 173/116 [761 Invent Susum" Mats, 1963.568.780 3 1971 Matsuo 173/116 Minami-Isshiki, Nagaizumi-cho, sumo'gunishlzuoka'ken' Japan Primary Examiner-Ernest R. Purser 22 Filed; Man 221973 Assistant Examiner-William IF. Pate, Ill

Attorney, Agent, or FirmKurt Kelman [57] ABSTRACT [30] ForeignApplication Priority Data Disclosed is a free-piston type, pneumaticallyoperated Apr. 3, 1972 Japan 47-33357 mPaC 100 comprising a tool cylinderand a pump cylinder both pneumatically and integrally connected. [52]U.S. Cl. 173/14; 173/1 16; 173/122 e eciprocation of the pump piston inthe pump cyl- [51] Int. Cl 825d 9/08 inder ll cause the massivefree-piston to rise and de- 158] Field of Search 173/116, 118, 122, 14;scend in the i001 cylinder, nd th fr -pist n will 60/531 538, 542, 543;91/396; 92/8, 85 hammer the shank of the chisel at the end of the downstroke. The unique design of' the pneumatic connec- [56] R f n Cit dtion between the top spaces of the tool and pump pis- UNITED STATESPATENTS tons permits the use of a heavier free-piston. and 964.8757/1910 Nathorst 60 537 hence the 'mpact power be accordmgly mcreased'974.267 11/1910 Hennessy et a1 173/116 5 Claims, 10 Drawing Figures 2 I10 s S 2 8 1 l3 PATENTEU APR 2 21975 sum 2 m PATENTEUAPRZZIHYS HEET 3 UF3 BHOHLS NOlSld IMPACT TOOL This invention relates to a free-pistontype. pneumatically operated impact tool, and more particularly to animprovement of the impact tool invented by the same inventor andpatented as Japanese Pat. No. 656,654.

BACKGROUND OF THE INVENTION:

The inventor proposed a pneumatically operated impact tool comprising anair pump cylinder having a pump piston slidably mounted therein. boththe cylinders pneumatically communicating with each other, thus causingthe normal reciprocation of the pump pis ton in the pump cylinder toinduce an anomalousreciprocation of the free-piston in the toolcylinder. More specifically, in the impact tool above mentioned thenormal reciprocation of the pump piston in the pump cylinder controlsthe movement of the free-piston in the tool cylinder in such a way thatit uses as much time as possible to reach the top of the tool cylinder,but uses as little time as possible to reach the bottom of the toolcylinder.

The impact tool proposed in the Japanese Patent above workssatisfactorily. However, if a free-piston of large mass is used in thehope of increasing the impact power generated thereby, it is difficultto retain such a heavy free-piston at the top dead point. and the use ofa heavy free-piston results in abnormal timing between the pistons and aconsequent loss of efficiency.

SUMMARY OF THE INVENTION The object of this invention is to provide apneumatically operated impact tool in which a massive freepiston iscontrolled so as to generate an increased impact power.

. To attain this object the pneumatically operated impact tool accordingto this invention comprises an air pump cylinder having a pump pistonslidably mounted therein; a tool cylinder having a free-piston slidablymounted therein; the head portion of said tool cylinder having anaperture and a uni-directional exhaust port, said free-piston having amale portion which is adapted to fit in and close said aperture of thehead portion; both said pump and tool cylinders being integrallyconnected and pneumatically communicating through a side opening made onthe adjacent side walls of the cylinder housings and at the same timethrough said aperture and uni-directional exhaust port and through an,upper tube whose opposite ends open at the upper spaces of saidcylinders; a chisel slidably mounted to the bottom of said tool cylinderand protruding therefrom into:said tool cylinder; and a crank mechanismoperatively connected to said pump piston.

BRIEF DESCRIPTION OF THE DRAWINGS The above and still further objects,features and advantages of this invention will be more apparent from thefollowing description when considered in connection with theaccompanying drawings in which:

FIG. I is a longitudinal sectional view of an embodiment of thepneumatically operated impact tool according to this invention in whichthe free-piston is at the bottom dead point whereas the pump piston isat the top dead point.

FIGS. 2-1 to 2-7 are the sequential operations of the pump piston andthe free-piston of this invention.

FIG. 3 is a graphic representation of the periodical movements of thefree-piston of the impact tool of this invention (solid line), thepumppiston of the same (broken line) and the free-piston of the JapanesePatent (chain line).

FIG. 4 is a longitudinal sectional view of another embodiment ofpneumatically operated impact tool according to this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS:

Referring to FIG. 1, l is a free-piston; 2 a tool cylinder whose headportion has an aperture 2' at the center thereof; 3 a pump piston; and 4a pump cylinder whose head portion has an aperture 4' at the centerthereof.

Both the cylinders 2 and 4 are parallel-arranged and integrallyconnected, communicating with each other by an upper tube 5 whoseopposite ends open at the apertures 2' and 4', and by a lower sideopening 6 which is provided to the lower portions of the adjacent innerwalls of the cylinders. The pump cylinder 4 has a crank casing 7 at thebottom end of the cylinder housing. A crank 8 contained in the crankcasing is connected to a piston 3 by a piston rod. Crank 8 is driven bymotor 14 through belt 15 and pulley 13. The chamber space defined by thecrank casing and by the pump cylinder is closed in air-tight fashionexcept for the top aperture 4' and the side opening 6.

The free-piston 1 has a male portion 10 which is adapted to fit in andclose the aperture 2 of the head portion when the free-piston reachesthe top level of the tool cylinder, and the head portion of the toolcylinder head a port 12, which is positioned in parallel relation withthe aperture 2 and contains a non-return valve means 11.

The free-piston 1 when driven downward. will strike against the end ofachisel 9 with a strong force before the free-piston reaches the bottomdead point.

Referring to FIGS. 2-1 to 2-7, FIG. 12-] shows the state of the toolbefore the start of the operation. and in this case the upper remainingspace 4a of the pump cylinder communicates with the upper remainingspace 2a of the tool cylinder through the upper tube 5 and the lowerremaining space 4b of the pump cylinder communicates with the upperremaining space 2a through the upper part of the opening 6 which is openwhen the free-piston l is at the bottom dead point. The freepiston 1thus is not influenced by the motion of the pump piston 3 which free toreciprocate in an idle state.

To start the free-piston 1, the chisel 9 is brought in contact with thematerial to be crushed to push the free-piston l upward to a positionwhere the bottom thereof is somewhat above the bottom of the sideopening 6 thus communicating thelower remaining space 2b of the toolcylinder with the lower remaining space 4b of the pump cylinder. (SeeFIG. 2-2) As the pump piston 3 moves downward it compresses the air inboth the lower remaining spaces 2b and 4b and reduces the pressure ofthe air in both the upper remaining spaces 20 and 4a. The positivepressure of the air thus compressed and the negative pressure of the airthus expanded cause the free-piston I to move upward. (See FIGS. 2-3)The free-piston 1 moves to the vicinity of the top dead point (See FIGS.2-4). and then the male portion 10 of the freepiston enters and closesthe aperture 2' of the head portion in an air-tight fashion, thuspreventing the air from passing to the upper space of the pump cylinderthrough the. upper tube 5. (At the same moment as the pump-piston is inthe vicinity of the bottom dead point.) As a result, the free-pistonrises at a reduced speed, compressing the air which is confined in theremaining space between the free-piston and the head portion of the toolcylinder. The pressure of the air confined and compressed in theremaining space 2a is so increased that it overcomes the counter springforce of the non-return valve 1 l, and then the valve 11 is opened,allowing the trapped air to flow from the remaining space 2a of the toolcylinder to the upper space 4a of the pump cylinder through the port 12.

While the trapped air is being released, the freepiston is still rising,purging the remaining air to the upper space 4a of the pump cylinder,and at the same time the free-piston is being cushioned until it reachesthe top dead point.

The free-piston 1 reaches its highest point at the time the pump piston3 reaches the bottom dead point. The pressure of the air trapped in theupper remaining space 2a is then reduced under the weight of the freepiston l.

The negative pressure due to this air will apply to the upper surface ofthe free-piston, and hence the freepiston is kept still at the top deadpoint, while the pump piston is rising to the top dead point (See FIGS.2-5).

As the pump piston 3 is moving to the vicinity of the top dead point(See FIGS. 2-6), the air is being compressed in the upper space 4a ofthe pump cylinder and in the upper tube 5 communicating therewith. Asshown in FIG. 1, the port 12 is closed by the ball 11, and therefore thepressure of the air thus compressed both in the upper space 40 and inthe tube 5 will apply to, the small surface of the male portion only.Because of the small surface area of the male portion 10, the pressureof air applied to each unit area of the whole upper surface of thefree-piston is ofa small fraction of the pressure of air applied to eachunit area of the male portion, and therefore the free-piston remains atthe top dead point under a state of suction, or sometimes the freepistonis allowed to descend somewhat, but the male portion thereof still doesnot leave the aperture 2' (See FIG. 2-7). When the pump piston reachesthe top dead point, and when the pressure of the air in the remainingupper space 4a is increased to the maximum, the free-piston startsdescending, the male portion leaves the apperture 2'. Thus, the maximumpositive pressure of air will apply to the whole upper surface of thefree-piston, and at the same time the maximum negative'pressure of theair in the remaining lower space of the pump cylinder will apply to thewhole lower surface of the free-piston through the side opening 6. Thefree-piston thus subjected to the push-pull action will be jerked,pulling the male portion clear of the aperture 2. The free-pistondescends at an increased speed until it strikes against the chisel 9(See FIG. 2-1), and then the upper space 2a of the tool cylindercommunicates with the lower space 417 of the pump cylinder, thusallowing the positive pressure of air to flow from the tool cylinder tothe lower space of the pump cylinder through the side opening 6.

The side opening 6 is somewhat shorter than the height of thefree-piston 1 and can be divided into two side openings as shown in FIG.4.

After hammering the chisel 9, the free-piston l is pushed upward by thechisel 9 which is still in contact with the material and by the reactionresulting from its impact with the chisel 9 (See FIG. 2-2). The bottomof the free-piston I thus passes above the bottom of side opening 6 sothat negative pressure is generated in the upper remaining space 2a andthe positive pressure is generated in the lower remaining space 4bcausing the free-piston l to rise as the pump piston 3 moves downward.(See FIGS. 2-3 to 2-4) Thus the impact motion repeats smoothly andcontinuously. The impact motion of the free-piston 1' can be stoppedonly by removing the chisel 9 from the material.

The central features of this invention as mentioned above can be reducedto:

i. the free-piston 1 has a male portion 10, which is adapted to fit inand close the aperture 2' of the head portion of the tool cylinder 2 inthe vicinity of the termination of the upward stroke of the freepistonI, thus closing the gas passage from the tool cylinder 2 to the pumpcylinder 4;

the head portion of the tool cylinder has an exhaust part 12 positionedadjacent to the aperture 2' of the head portion thus allowing, after theclosure by the male portion of the aperture 2, the freepiston to riseand compress the air confined in the upper remaining space 2a of thetool cylinder 2 until the pressure of the air thus compressed causes theassociated non-return valve to open, and at the same time thus allowingthe free-piston to rise and purge the remaining air into the gas passageto the upper space of the piston cylinder until it reaches the top deadpoint and is held there under suction;

iii. the free-piston 1 will not start descending before the pump piston3 has compressed the air confined in the remaining upper space of thepiston cylinder 4 to the maximum because the pressure of the compressedair is applied to the large upper surface of the free-piston only viathe small top surface of the male portion.

The result attained thereby is shown in FIG. 3, particularly, around thetop dead point of the stroke of the free-piston. The ramps B, H of thecurve (solid line) around the top dead point in FIG. 3 indicates thatthis invention permits the use of a freepiston which is heavier thanthat of the conventional machine, and hence the impact or smashing powerof the chisel is substantially increased.

What is claimed is:

1. A pneumatic impact tool comprising in combination:

A. an air pump cylinder having a pump piston slidably disposed therein,and crank mechanism means for slidably moving said pump piston;

B. a tool cylinder having a free-piston slidably disposed therein, saidtool cylinder having an aperture on the head portion thereof and aunidirectional port means which allows air to pass from said toolcylinder to said pump cylinder through said upper tube housing, butprevents air from otherwise passing, said free-piston having a malemember disposed to pneumatically close the aperture;

C. an upper tube housing pneumatically connecting the upper portion ofthe air pump cylinder and, the aperture and unidirectional exhaust portof the tool cylinder; 3

D. a common side wall opening joining the lower portion of the air pumpcylinder and the lower portion of the tool cylinder said opening havinga height less than the height of the free-piston and disposed to permita free pneumatic opening when the freepiston is at the bottom dead pointwithin the tool cylinder; and

E. a chisel slidably mounted into the bottom of said tool cylinder andprotruding therefrom, said chisel contacting the free-piston and movablethereagainst for placing the free-piston in position to top thereof whenthe free-piston reaches the bottom dead point and is closed when thefree-piston is elevated by the chisel, the pump piston being permittedto slidably operate in idle state when the free-piston is at the bottomdead point without effecting pneumatic movement of the free-piston.

4. A pneumatic impact tool according to claim 1 wherein the bottomsurface of said free-piston has a counter sunk recess to accomodate theend of said chisel when said free-piston strikes against said chisel.

5. A pneumatic impact tool according to claim 1 wherein said common sidewall opening is formed of two sections, one of which openings is sealedwhen the free-piston is at the bottom dead point.

1. A pneumatic impact tool comprising in combination: A. an air pumpcylinder having a pump piston slidably disposed therein, and crankmechanism means for slidably moving said pump piston; B. a tool cylinderhaving a free-piston slidably disposed therein, said tool cylinderhaving an aperture on the head portion thereof and a unidirectional portmeans which allows air to pass from said tool cylinder to said pumpcylinder through said upper tube housing, but prevents air fromotherwise passing, said free-piston having a male member disposed topneumatically close the aperture; C. an upper tube housing pneumaticallyconnecting the upper portion of the air pump cylinder and, the apertureand unidirectional exhaust port of the tool cylinder; D. a common sidewall opening joining the lower portion of the air pump cylinder and thelower portion of the tool cylinder said opening having a height lessthan the height of the freepiston and disposed to permit a freepneumatic opening when the free-piston is at the bottom dead pointwithin the tool cylinder; and E. a chisel slidably mounted into thebottom of said tool cylinder and protruding therefrom, said chiselcontacting the free-piston and movable thereagainst for placing thefreepiston in position to pneumatically seal said common side wallopening whereby pneumatic movement of the free-piston is initiated.
 1. Apneumatic impact tool comprising in combination: A. an air pump cylinderhaving a pump piston slidably disposed therein, and crank mechanismmeans for slidably moving said pump piston; B. a tool cylinder having afree-piston slidably disposed therein, said tool cylinder having anaperture on the head portion thereof and a unidirectional port meanswhich allows air to pass from said tool cylinder to said pump cylinderthrough said upper tube housing, but prevents air from otherwisepassing, said free-piston having a male member disposed to pneumaticallyclose the aperture; C. an upper tube housing pneumatically connectingthe upper portion of the air pump cylinder and, the aperture andunidirectional exhaust port of the tool cylinder; D. a common side wallopening joining the lower portion of the air pump cylinder and the lowerportion of the tool cylinder said opening having a height less than theheight of the free-piston and disposed to permit a free pneumaticopening when the free-piston is at the bottom dead point within the toolcylinder; and E. a chisel slidably mounted into the bottom of said toolcylinder and protruding therefrom, said chisel contacting thefree-piston and movable thereagainst for placing the free-piston inposition to pneumatically seal said common side wall opening wherebypneumatic movement of the free-piston is initiated.
 2. A pneumatic toolaccording to claim 1 wherein said unidirectional exhaust port comprisesan aperture to communicate with said upper tube housing and a non-returnvalve.
 3. A pneumatic impact tool according to claim 1 wherein saidcommon side wall opening is open at the top thereof when the free-pistonreaches the bottom dead point and is closed when the free-piston iselevated by the chisel, the pump piston being permitted to slidablyoperate in idle state when the free-piston is at the bottom dead pointwithout effecting pneumatic movement of the free-piston.
 4. A pneumaticimpact tool according to claim 1 wherein the bottom surface of saidfree-piston has a counter sunk recess to accomodate the end of saidchisel when said free-piston strikes against said chisel.